The focus of this article is an examination of chemical reaction mechanisms in ionic liquids. These mechanisms are compared with those pertaining to the same reactions carried out in conventional solvents. In cases where the mechanisms differ, attempts to provide an explanation in terms of the chemical and physicochemical properties of the reactants and of the components of the ionic liquids are described. A wide range of reactions from different branches of chemistry has been selected for this purpose. A sufficient background for student readers has been included. This tutorial review should also be of interest to kineticists, and to both new and experienced investigators in the ionic liquids field.

A brief overview of mechanistic studies on the reactions of different Pt(II) complexes with nitrogen- and sulfur-donor biomolecules is presented. The first part describes the results obtained for substitution reactions of mono-functional Pt(II) complexes with different biomolecules, under various experimental conditions (temperature, pH and ionic strength). In addition, an overview of the results obtained for the substitution reactions of bi-functional Pt(II) complexes, analogous to cisplatin, with biomolecules is given. The last part of this report deals with different polynuclear Pt(II) complexes and their substitution behaviour with different biomolecules. The purpose of this perspective is to improve the understanding of the mechanism of action of Pt(II) complexes as potential anti-tumour drugs in the human body.

The blue copper protein from Pseudomonas aeruginosa , azurin, immobilized at gold electrodes through hydrophobic interaction with alkanethiol self-assembled monolayers (SAMs) of the general type [-S - (CH ₂ ) _n - CH ₃ ] ( n = 4, 10, and 15) was employed to gain detailed insight into the physical mechanisms of short- and long-range biomolecular electron transfer (ET). Fast scan cyclic voltammetry and a Marcus equation analysis were used to determine unimolecular standard rate constants and reorganization free energies for variable n , temperature (2–55 °C), and pressure (5–150 MPa) conditions. A novel global fitting procedure was found to account for the reduced ET rate constant over almost five orders of magnitude (covering different n , temperature, and pressure) and revealed that electron exchange is a direct ET process and not conformationally gated. All the ET data, addressing SAMs with thickness variable over ca. 12 Å, could be described by using a single reorganization energy (0.3 eV), however, the values for the enthalpies and volumes of activation were found to vary with n . These data and their comparison with theory show how to discriminate between the fundamental signatures of short- and long-range biomolecular ET that are theoretically anticipated for the adiabatic and nonadiabatic ET mechanisms, respectively.

A remarkably efficient, catalytic oxidative degradation of Orange II in aqueous solution was observed in the presence of simple Mn(II) salts used in combination with the green oxidant peracetic acid (PAA) under mild reaction conditions at pH 9.5 and 25 °C. In order to gain further insight into the complex reaction network responsible for the fast and efficient degradation of Orange II, detailed kinetic studies on the catalytic degradation reaction were performed. The influence of the catalyst, oxidant, and buffer concentrations on the reaction course was studied in detail by in situUV/Vis spectroscopy. The degradation rate increased with increasing catalyst and PAA concentration, decreased with increasing carbonate buffer concentration, and the reaction showed maximum reactivity at pH ≈ 9.4. Studies performed in the absence of substrate revealed the successive formation of various high valence manganese intermediates under the selected experimental conditions. The UV/Vis spectral changes observed upon addition of PAA to a Mn(II) ion containing solution at pH 9.5 showed biphasic behavior, and led to the formation of Mn^VIIO₄ ⁻ and colloidal Mn^IVO₂ as final products. Through the combination of EPR and UV/Vis spectroscopy, the presence of a Mn(IV) species during the first phase of the reaction was observed. If the addition of a dye to the Mn(II)/PAA containing reaction mixture was carried out after different delay times during the course of the reaction, significant changes observed in the degradation performance pointed to changes in the catalyst composition with time. Thereby, the highest reactivity was reached just before the formation of the high valence intermediates and colloidal Mn^IVO₂ occurred. Selected catalytic experiments with different in situ formed intermediates showed the essential role of a small amount of hydrogen peroxide (omnipresent in commercial peracetic acid, 6 wt% H₂O₂) for efficient catalytic dye decomposition. H₂O₂ was shown to play a crucial role as a reducing agent in the catalytic cycle, avoiding the over-oxidation of the catalyst, and thereby extending the lifetime of the catalytic system. The data were evaluated to gain mechanistic insight into the complex chemical reactions occurring during the Mn(II) catalyzed oxidative dye degradation with PAA. A comparison with earlier results concerning the use of H₂O₂/HCO₃ ⁻ as oxidant was made.

Urease, a Ni-containing metalloenzyme, features an activity that has profound medical and agricultural implications. The mechanism of this activity, however, has not been as yet thoroughly established. Accordingly, to improve its understanding, in this study we analyzed the steady-state kinetic parameters of the enzyme (jack bean), K _M and k _cat, measured at different temperatures and pressures. Such an analysis is useful as it provides information on the molecular nature of the intermediate and transition states of the catalytic reaction. We measured the parameters in a noninteracting buffer using a stopped-flow technique in the temperature range 15–35 °C and in the pressure range 5–132 MPa, the pressure-dependent measurements being the first of their kind performed for urease. While temperature enhanced the activity of urease, pressure inhibited the enzyme; the inhibition was biphasic. Analyzing K _M provided the characteristics of the formation of the ES complex, and analyzing k _cat, the characteristics of the activation of ES. From the temperature-dependent measurements, the energetic parameters were derived, i.e. thermodynamic ΔH ^o and ΔS ^o for ES formation, and kinetic ΔH ^≠ and ΔS ^≠ for ES activation, while from the pressure-dependent measurements, the binding ΔV _b and activation \( \Updelta V_{\rm cat}^{ \ne } \) volumes were determined. The thermodynamic and activation parameters obtained are discussed in terms of the current proposals for the mechanism of the urease reaction, and they are found to support the mechanism proposed by Benini et al. (Structure 7:205–216; 1999), in which the Ni–Ni bridging hydroxide—not the terminal hydroxide—is the nucleophile in the catalytic reaction. Graphical abstract